In the United States and most regions around the world, many farms suffer from low phosphorus (P) use efficiency, meaning that P inputs (fertilizer or manure) are greater than the P harvested in crops. Even when seemingly adequate P fertilizer is applied to soils, 70-90% can quickly become unavailable for plant uptake. This is largely because P readily sorbs to weathered mineral surfaces within the soil profile. Over time, this creates large pools of residual soil P that is unavailable for plant uptake. In response, farmers often apply P fertilizer in excess of plant requirements, which contributes to P runoff into groundwater and eutrophication of aquatic ecosystems.
Environmental awareness, resource constraints, and general public opinion are increasing the demand for efficient green technologies and products as options to traditional P fertilizer. Such green technologies and products are those that promote sustainability and have minimal impact on the environment. One area that is being exploited to develop green technology and products is the use of microorganisms and their specialized properties. While most soil P is unavailable to plants, some microorganisms have the ability to solubilize inorganic P and other micronutrients and mineralize organic P into soluble orthophosphate that is available for plant uptake. Collectively, these two processes mobilize soil phosphorus, increasing its availability to plants.
Other isolates of bacteria and fungi have also been reported to mobilize phosphorus. While there is great potential to improve microbial P mobilization, progress in commercializing microbial compositions has been largely limited. In some cases, commercial bacterial inoculants cannot significantly enhance P availability or plant growth even at high use concentrations, due to instability under certain conditions such as high temperature and high pH, and by the identification of single strains through traditional culturing techniques for use in the inoculants. Use of combinations of at least two bacteria isolates can improve activity, broaden potential applications, reduce use concentrations and costs, and reduce the need for chemical fertilizer inputs. Combinations of different bacteria isolates further can provide enhanced performance in a broader range of soils and climates due to functional redundancy. There are many other microbial inoculants on the market that claim to stimulate plant health. These products contain an undefined mixture of microbes that are grown on organic waste products, and are essentially a compost tea with no defined mechanistic functionality. While they make broad claims, these products are not very effective and have only penetrated a niche market of enthusiasts.
Accordingly, there is a need to develop microorganism-based technologies and products for P mobilization that are stable under various conditions, have an appreciable shelf life, combine two or more strains, and increase plant growth and health while reducing chemical inputs and environmental impact.